ORCID Profile
0000-0002-8444-2775
Current Organisations
The University of Newcastle
,
University of Newcastle Australia
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Research Topics
In Research Link Australia (RLA), "Research Topics" refer to ANZSRC FOR and SEO codes. These topics are either sourced from ANZSRC FOR and SEO codes listed in researchers' related grants or generated by a large language model (LLM) based on their publications.
Top 5 Research Topics
ANZSRC Field of Research (FoR)
Quantum Chemistry | Theoretical and Computational Chemistry not elsewhere classified | Computational chemistry | Materials engineering | Colloid and surface chemistry | Colloid and Surface Chemistry | Macromolecular and Materials Chemistry | Synthesis of Materials | Theoretical and Computational Chemistry | Physical Chemistry (Incl. Structural) | Nanomaterials | Functional materials | Physical chemistry | Photonics optoelectronics and optical communications | Mineral Processing/Beneficiation | Resources Engineering and Extractive Metallurgy | Nanofabrication, Growth and Self Assembly
ANZSRC Socio-Economic Objective (SEO)
Expanding Knowledge in the Chemical Sciences | Expanding Knowledge in the Physical Sciences | First Stage Treatment of Ores and Minerals not elsewhere classified | Expanding Knowledge in Technology | Concentrating Processes of Base Metal Ores (excl. Aluminium and Iron Ores) |
Related Links
Publications
Ab initio electronic and rovibrational structure of
Publisher: Elsevier BV
Date: 07-2008
Electronic structure and high-temperature thermochemistry of BaZrO3−δ perovskite from first-principles calculations
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C9CP02505G
Abstract: Accurate first-principles calculations predict electronic structure and high-temperature thermochemical properties of oxygen-deficient BaZrO 3 .
A graph neural network model with local environment pooling for predicting adsorption energies
Publisher: Elsevier BV
Date: 08-2023
Performance of DFT for C60 Isomerization Energies: A Noticeable Exception to Jacob’s Ladder
Publisher: American Chemical Society (ACS)
Date: 06-12-2019
Abstract: The ability to accurately calculate relative energies of fullerenes is important in many areas of computational nanotechnology. Because of the large size of fullerenes, their relative energies cannot normally be calculated by means of high-level ab initio procedures, and therefore, density functional theory (DFT) represents a cost-effective alternative. In an extensive benchmark study, we calculate the electronic energies of eight C
Erratum: “DFTB+, a software package for efficient approximate density functional theory based atomistic simulations” [J. Chem. Phys. 152, 124101 (2020)]
Publisher: AIP Publishing
Date: 18-07-2022
DOI: 10.1063/5.0103026
Front Cover: Defect Engineering for Photocatalysis: From Ternary to Perovskite Oxynitrides (ChemNanoMat 5/2020)
Publisher: Wiley
Date: 28-04-2020
Combined STM, AFM, and DFT Study of the Highly Ordered Pyrolytic Graphite/1-Octyl-3-methyl-imidazolium Bis(trifluoromethylsulfonyl)imide Interface
Publisher: American Chemical Society (ACS)
Date: 12-05-2014
DOI: 10.1021/JP501260T
Nucleation of Graphene Precursors on Transition Metal Surfaces: Insights from Theoretical Simulations
Publisher: American Chemical Society (ACS)
Date: 05-07-2013
DOI: 10.1021/JP404326D
Ab initio study of ground state MH2, HMHe+ and MHe22+, M = Mg, Ca
Publisher: Royal Society of Chemistry (RSC)
Date: 2008
DOI: 10.1039/B710310G
Abstract: The ground states of MH2, HMHe+ and MHe2(2+) (M = Mg, Ca) have been investigated using relativistically-corrected CCSD(T), IC-MRCI and IC-MRCI+Q, in conjunction with ANO-RCC (Mg, Ca) and aug-cc-pVQZ (H, He) basis sets. The ground states of all magnesium species are predicted to be linear, in agreement with predicted trends. Conversely, HCaHe+ and CaHe2(2+) were determined to be quasi-linear species, with linear-inversion barriers of ca. 115 and 3 cm(-1), respectively. For CaH2, a stationary point on the molecular potential energy surface corresponding to a non-linear equilibrium structure was not observed. Trends in bonding, dissociative potential well-depths and spectroscopic constants for these species have been considered with regards to isoelectronic and isovalent reasoning. These trends are consistent with helium and hydrogen forming electrostatic and covalent bonds with the metal ion, respectively.
Role of Graphitic Bowls in Temperature Dependent Fullerene Formation
Publisher: American Chemical Society (ACS)
Date: 30-11-2022
Abstract: Fullerenes are used extensively in organic electronics as electron acceptors among other uses however, there are still several key mysteries regarding their formation such as the importance of graphitic intermediates and the thermokinetics of initial cage formation. To this end, we have conducted density functional tight binding molecular dynamics (DFTB-MD) calculations on disintegrated
Hofmeister effects influence bulk nanostructure in a protic ionic liquid
Publisher: Elsevier BV
Date: 09-2023
Step-edge self-assembly during graphene nucleation on a nickel surface: QM/MD simulations
Publisher: Royal Society of Chemistry (RSC)
Date: 2014
DOI: 10.1039/C3NR04694J
Abstract: Quantum chemical molecular dynamics simulations of graphene nucleation on the Ni(111) surface show that graphene creates its own step-edge as it forms. This "step-edge self-assembly" is driven by the formation of thermodynamically favorable Ni-C σ-bonds at the graphene edge. This dynamic aspect of the Ni(111) catalyst is in contrast to the commonly accepted view that graphene nucleates on a pre-existing, static catalyst step-edge. Simulations also show that, simply by manipulating the subsurface carbon density, preferential formation of single-layer graphene instead of multi-layer graphene can be achieved on nickel catalysts.
Low-Cost Pt Alloys for Heterogeneous Catalysis Predicted by Density Functional Theory and Active Learning
Publisher: American Chemical Society (ACS)
Date: 28-07-2021
Ab initio calculations of the electronic structure of the ground states of HBeHe+ and BeHe2 2 +
Publisher: Elsevier BV
Date: 07-2007
Quantum Chemical Simulation of Carbon Nanotube Nucleation on Al2O3 Catalysts via CH4 Chemical Vapor Deposition
Publisher: American Chemical Society (ACS)
Date: 22-07-2015
DOI: 10.1021/JACS.5B02952
Abstract: We present quantum chemical simulations demonstrating how single-walled carbon nanotubes (SWCNTs) form, or "nucleate", on the surface of Al2O3 nanoparticles during chemical vapor deposition (CVD) using CH4. SWCNT nucleation proceeds via the formation of extended polyyne chains that only interact with the catalyst surface at one or both ends. Consequently, SWCNT nucleation is not a surface-mediated process. We demonstrate that this unusual nucleation sequence is due to two factors. First, the π interaction between graphitic carbon and Al2O3 is extremely weak, such that graphitic carbon is expected to desorb at typical CVD temperatures. Second, hydrogen present at the catalyst surface actively passivates dangling carbon bonds, preventing a surface-mediated nucleation mechanism. The simulations reveal hydrogen's reactive chemical pathways during SWCNT nucleation and that the manner in which SWCNTs form on Al2O3 is fundamentally different from that observed using "traditional" transition metal catalysts.
Energy and Charge Transfer at the Boron Nitride Nanotube—Catalyst Growth Interface
Publisher: American Chemical Society (ACS)
Date: 29-04-2020
Scalable growth of single-walled carbon nanotubes with a highly uniform structure
Publisher: Royal Society of Chemistry (RSC)
Date: 2020
DOI: 10.1039/D0NR01919D
Abstract: Structure-controlled growth of single-walled carbon nanotubes by floating catalyst CVD.
Do SiO2 and carbon-doped SiO2 nanoparticles melt? Insights from QM/MD simulations and ramifications regarding carbon nanotube growth
Publisher: Elsevier BV
Date: 05-2011
Specific Ion Effects at the Vapor–Formamide Interface: A Reverse Hofmeister Series in Ion Concentration Depth Profiles
Publisher: American Chemical Society (ACS)
Date: 29-08-2023
Single-walled Carbon Nanotube Growth from Chiral Carbon Nanorings: Prediction of Chirality and Diameter Influence on Growth Rates
Publisher: American Chemical Society (ACS)
Date: 14-09-2012
DOI: 10.1021/JA305769V
Abstract: Catalyst-free, chirality-controlled growth of chiral and zigzag single-walled carbon nanotubes (SWCNTs) from organic precursors is demonstrated using quantum chemical simulations. Growth of (4,3), (6,5), (6,1), (10,1) and (8,0) SWCNTs was induced by ethynyl radical (C(2)H) addition to organic precursors. These simulations show a strong dependence of the SWCNT growth rate on the chiral angle, θ. The SWCNT diameter however does not influence the SWCNT growth rate under these conditions. This agreement with a previously proposed screw-dislocation-like model of transition metal-catalyzed SWCNT growth rates [Ding, F. Proc. Natl. Acad. Sci. 2009, 106, 2506] indicates that the SWCNT growth rate is an intrinsic property of the SWCNT edge itself. Conversely, we predict that the rate of SWCNT growth via Diels-Alder cycloaddition of C(2)H(2) is strongly influenced by the diameter of the SWCNT. We therefore predict the existence of a maximum growth rate for an optimum diameter/chirality combination at a given C(2)H/C(2)H(2) ratio. We also find that the ability of a SWCNT to avoid defect formation during growth is an intrinsic quality of the SWCNT edge.
Boron Nitride Nanotube Nucleation via Network Fusion during Catalytic Chemical Vapor Deposition
Publisher: American Chemical Society (ACS)
Date: 07-08-2019
DOI: 10.1021/JACS.9B03484
Abstract: Despite boron nitride nanotubes (BNNTs) first being synthesized in the 1990s, their nucleation mechanism remains unknown. Here we report nonequilibrium molecular dynamics simulations showing how BNNT cap structures form during Ni-catalyzed chemical vapor deposition (CVD) of ammonia borane. BN hexagonal ring networks are produced following the catalytic evolution of H
Effect of ammonia on chemical vapour deposition and carbon nanotube nucleation mechanisms
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C6NR08222J
Abstract: Chemical vapour deposition (CVD) growth of carbon nanotubes is currently the most viable method for commercial-scale nanotube production. However, controlling the 'chirality', or helicity, of carbon nanotubes during CVD growth remains a challenge. Recent studies have shown that adding chemical 'etchants', such as ammonia and water, to the feedstock gas can alter the diameter and chirality of nanotubes produced with CVD. To date, this strategy for chirality control remains sub-optimal, since we have a poor understanding of how these etchants change the CVD and nucleation mechanisms. Here, we show how ammonia alters the mechanism of methane CVD and single-walled carbon nanotube nucleation on iron catalysts, using quantum chemical molecular dynamics simulations. Our simulations reveal that ammonia is selectively activated by the catalyst, and this enables ammonia to play a dual role during methane CVD. Following activation, ammonia nitrogen removes carbon from the catalyst surface exclusively via the production of hydrogen (iso)cyanide, thus impeding the growth of extended carbon chains. Simultaneously, ammonia hydrogen passivates carbon dangling bonds, which impedes nanotube nucleation and promotes defect healing. Combined, these effects lead to slower, more controllable nucleation and growth kinetics.
Crystalline Ni3C as both carbon source and catalyst for graphene nucleation: a QM/MD study
Publisher: Springer Science and Business Media LLC
Date: 14-07-2015
DOI: 10.1038/SREP12091
Abstract: Graphene nucleation from crystalline Ni 3 C has been investigated using quantum chemical molecular dynamics (QM/MD) simulations based on the self-consistent-charge density-functional tight-binding (SCC-DFTB) method. It was observed that the lattice of Ni 3 C was quickly relaxed upon thermal annealing at high temperature, resulting in an amorphous Ni 3 C catalyst structure. With the aid of the mobile nickel atoms, inner layer carbon atoms precipitated rapidly out of the surface and then formed polyyne chains and Y-junctions. The frequent sinusoidal-like vibration of the branched carbon configurations led to the formation of nascent graphene precursors. In light of the rapid decomposition of the crystalline Ni 3 C, it is proposed that the crystalline Ni 3 C is unlikely to be a reaction intermediate in the CVD-growth of graphene at high temperatures. However, results present here indicate that Ni 3 C films can be employed as precursors in the synthesis of graphene with exciting possibility.
Polyyne Chain Growth and Ring Collapse Drives Ni-Catalyzed SWNT Growth: A QM/MD Investigation
Publisher: American Chemical Society (ACS)
Date: 02-04-2010
DOI: 10.1021/JP100790E
Defect Healing during Single-Walled Carbon Nanotube Growth: A Density-Functional Tight-Binding Molecular Dynamics Investigation
Publisher: American Chemical Society (ACS)
Date: 08-09-2009
DOI: 10.1021/JP9053549
Anion ordering and vacancy defects in niobium perovskite oxynitrides
Publisher: Royal Society of Chemistry (RSC)
Date: 2021
DOI: 10.1039/D1MA00122A
Abstract: First-principles calculations predict the stability and mobility of vacancy defects in niobium perovskite oxynitrides, aiding defect engineering for enhanced photocatalysis.
Nanostructure of Deep Eutectic Solvents at Graphite Electrode Interfaces as a Function of Potential
Publisher: American Chemical Society (ACS)
Date: 21-01-2016
Revealing the Dual Role of Hydrogen for Growth Inhibition and Defect Healing in Polycyclic Aromatic Hydrocarbon Formation: QM/MD Simulations
Publisher: American Chemical Society (ACS)
Date: 07-2013
DOI: 10.1021/JZ400925F
Ion specificity in the measured concentration depth profile of ions at the Vapor-Glycerol interface
Publisher: Elsevier BV
Date: 11-2022
DOI: 10.1016/J.JCIS.2022.06.104
Abstract: Specific ion effects are manifest universally across many systems and solvents. Whilst broad understanding of these effects is emerging particularly for bulk effects, the perturbation introduced by the interfaces are generally not understood. We hypothesise that through a careful investigation of the distribution of ions at the glycerol-vapor interface we can better understand specific ion effects in this system and at interfaces. Neutral impact collision ion scattering spectroscopy (NICISS) is used to obtain and compare in idual ion concentration depth profiles (CDP) for a range of monovalent inorganic anions and cations at 12 glycerol electrolyte solutions surfaces. The distribution of ions at the vapor - glycerol interface is non-monotonic. Broadly, anions are concentrated at the outermost region of the interface and cations are depleted from the interface. The distribution of Cl
Polymer solvation in choline chloride deep eutectic solvents modulated by the hydrogen bond donor
Publisher: Elsevier BV
Date: 04-2019
Structure and absorption in C60–zinc tetra-phenylporphyrin composite materials: A computational study
Publisher: Elsevier BV
Date: 2015
DFTB+, a software package for efficient approximate density functional theory based atomistic simulations
Publisher: AIP Publishing
Date: 23-03-2020
DOI: 10.1063/1.5143190
Abstract: DFTB+ is a versatile community developed open source software package offering fast and efficient methods for carrying out atomistic quantum mechanical simulations. By implementing various methods approximating density functional theory (DFT), such as the density functional based tight binding (DFTB) and the extended tight binding method, it enables simulations of large systems and long timescales with reasonable accuracy while being considerably faster for typical simulations than the respective ab initio methods. Based on the DFTB framework, it additionally offers approximated versions of various DFT extensions including hybrid functionals, time dependent formalism for treating excited systems, electron transport using non-equilibrium Green’s functions, and many more. DFTB+ can be used as a user-friendly standalone application in addition to being embedded into other software packages as a library or acting as a calculation-server accessed by socket communication. We give an overview of the recently developed capabilities of the DFTB+ code, demonstrating with a few use case ex les, discuss the strengths and weaknesses of the various features, and also discuss on-going developments and possible future perspectives.
High-Throughput Aqueous Electrolyte Structure Prediction Using IonSolvR and Equivariant Graph Neural Network Potentials
Publisher: American Chemical Society (ACS)
Date: 16-10-2023
Insights into carbon nanotube and graphene formation mechanisms from molecular simulations: a review
Publisher: IOP Publishing
Date: 02-2015
DOI: 10.1088/0034-4885/78/3/036501
Abstract: The discovery of carbon nanotubes (CNTs) and graphene over the last two decades has heralded a new era in physics, chemistry and nanotechnology. During this time, intense efforts have been made towards understanding the atomic-scale mechanisms by which these remarkable nanostructures grow. Molecular simulations have made significant contributions in this regard indeed, they are responsible for many of the key discoveries and advancements towards this goal. Here we review molecular simulations of CNT and graphene growth, and in doing so we highlight the many invaluable insights gained from molecular simulations into these complex nanoscale self-assembly processes. This review highlights an often-overlooked aspect of CNT and graphene formation-that the two processes, although seldom discussed in the same terms, are in fact remarkably similar. Both can be viewed as a 0D → 1D → 2D transformation, which converts carbon atoms (0D) to polyyne chains (1D) to a complete sp(2)-carbon network (2D). The difference in the final structure (CNT or graphene) is determined only by the curvature of the catalyst and the strength of the carbon-metal interaction. We conclude our review by summarizing the present shortcomings of CNT/graphene growth simulations, and future challenges to this important area.
Dynamics of Local Chirality during SWCNT Growth: Armchair versus Zigzag Nanotubes
Publisher: American Chemical Society (ACS)
Date: 22-05-2012
DOI: 10.1021/JA301299T
Abstract: We present an analysis of the dynamics of single-walled carbon nanotube (SWCNT) chirality during growth, using the recently developed local chirality index (LOCI) method [ Kim et al. Phys. Rev. Lett. 2011 , 107 , 175505 ] in conjunction with quantum chemical molecular dynamics (QM/MD) simulations. Using (5,5) and (8,0) SWCNT fragments attached to an Fe(38) catalyst nanoparticle, growth was induced by periodically placing carbon atoms at the edge of the SWCNT. For both armchair and zigzag SWCNTs, QM/MD simulations indicate that defect healing-the process of defect removal during growth-is a necessary, but not sufficient, condition for chirality-controlled SWCNT growth. Time-evolution LOCI analysis shows that healing, while restoring the pristine hexagon structure of the growing SWCNT, also leads to changes in the local chirality of the SWCNT edge region and thus of the entire SWCNT itself. In this respect, we show that zigzag SWCNTs are significantly inferior in maintaining their chirality during growth compared to armchair SWCNTs.
Improved Representations of Heterogeneous Carbon Reforming Catalysis Using Machine Learning
Publisher: American Chemical Society (ACS)
Date: 10-09-2019
Abstract: Predicting adsorption energies of reaction intermediates is critical for determining catalytic reaction mechanisms. Here, we present three combined representations for predicting adsorption energies of carbon reforming species on transition-metal surfaces. Among the three combined representations, the Elemental Properties and Spectral London Axilrod-Teller-Muto (EP M) representation, which uses separate EP and SLATM representations for the surface and adsorbates, yields the lowest mean absolute error (MAE) of ∼0.18 eV with respect to density functional theory (DFT) adsorption formation energies for 68 adsorbates on four low-index metal facets (Cu(111), Pt(111), Pd(111), Ru(0001)). All three combined representations also have lower MAEs compared with linear scaling relations. Notably, two of the combined representations achieve their results using empirical/experimental molecular structures only (i.e., without recourse to structural optimization based on first-principles methods such as DFT). The combined representations enable improved efficiency for predicting heterogeneous catalytic mechanisms using machine learning approaches, largely bypassing expensive electronic structure calculations. Further, we show that the combined representations enable "cross-surface" training with regression and tree-based machine learning methods. That is, to predict adsorption formation energies on a particular catalyst metal, these methods only need a small amount of training s les (20%) on that metal.
Vacancy diffusion barriers in TaON and Ta3N5 water-splitting photocatalysts
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C9TA02280E
Abstract: First principles calculations reveal charge-dependent vacancy diffusion mechanisms in mixed anion photocatalytic materials.
SWNT Nucleation from Carbon-Coated SiO2 Nanoparticles via a Vapor−Solid−Solid Mechanism
Publisher: American Chemical Society (ACS)
Date: 10-12-2010
DOI: 10.1021/JA109018H
Abstract: Since the discovery of single-walled carbon nanotubes (SWNTs) in the early 1990s, the most commonly accepted model of SWNT growth on traditional catalysts (i.e., transition metals including Fe, Co, Ni, etc.) is the vapor-liquid-solid (VLS) mechanism. In more recent years, the synthesis of SWNTs on nontraditional catalysts, such as SiO(2), has also been reported. The precise atomistic mechanism explaining SWNT growth on nontraditional catalysts, however, remains unknown. In this work, CH(4) chemical vapor deposition (CVD) and single-walled carbon nanotube (SWNT) nucleation on SiO(2) nanoparticles have been investigated using quantum-chemical molecular dynamics (QM/MD) methods. Upon supply of CH(x) species to the surface of a model SiO(2) nanoparticle, CO was produced as the main chemical product of the CH(4) CVD process, in agreement with a recent experimental investigation [Bachmatiuk et al., ACS Nano 2009, 3, 4098]. The production of CO occurred simultaneously with the carbothermal reduction of the SiO(2) nanoparticle. However, this reduction, and the formation of amorphous SiC, was restricted to the nanoparticle surface, with the core of the SiO(2) nanoparticle remaining oxygen-rich. In cases of high carbon concentration, SWNT nucleation then followed, and was driven by the formation of isolated sp(2)-carbon networks via the gradual coalescence of adjacent polyyne chains. These simulations indicate that the carbon saturation of the SiO(2) surface was a necessary prerequisite for SWNT nucleation. These simulations also indicate that a vapor-solid-solid mechanism, rather than a VLS mechanism, is responsible for SWNT nucleation on SiO(2). Fundamental differences between SWNT nucleation on nontraditional and traditional catalysts are therefore observed.
Stochastic structure determination for conformationally flexible heterogenous molecular clusters: Application to ionic liquids
Publisher: Wiley
Date: 26-08-2013
DOI: 10.1002/JCC.23420
Abstract: We present a novel method that enables accurate and efficient computational determination of conformationally flexible clusters, "Kick(3)" This method uses stochastically generated structures in combination with fast quantum mechanical methods. We demonstrate the power of this method by elucidating the structure of ionic liquid (IL) ([xMIM(+)][NO3(-)])n clusters (x = E, B, D, n = 1-10,15). Dispersion-corrected, third-order self-consistent-charge density-functional tight-binding (DFTB3) is shown to be a computationally efficient, yet reliable approximation to density functional theory for predicting and understanding IL structure and stability. The presented approach, therefore, enables the accurate and efficient screening of ILs with high potential toward practical applications, without recourse to more expensive quantum chemical methods.
Ab Initio rovibrational spectrum of the NaH2 + ion–quadrupole complex
Publisher: Springer Science and Business Media LLC
Date: 12-11-2008
Understanding specific ion effects and the Hofmeister series
Publisher: Royal Society of Chemistry (RSC)
Date: 2022
DOI: 10.1039/D2CP00847E
Abstract: This perspective reviews the historical explanations for specific ion effects, and explores the frontiers of the field before summarising its challenges and opportunities.
Theoretical analysis of structural diversity of covalent organic framework: Stacking isomer structures thermodynamics and kinetics
Publisher: Elsevier BV
Date: 11-2016
Effect of halides on the solvation of poly(ethylene oxide) in the ionic liquid propylammonium nitrate.
Publisher: Elsevier BV
Date: 2019
DOI: 10.1016/J.JCIS.2018.09.057
Abstract: The solvation characteristics of poly(ethylene oxide) (PEO) in nanostructured protic ionic liquids (PILs) are driven by polymer-solvent interactions in the polar domains of the PIL. This work hypothesises that the nanostructure of a PIL can be altered via halide addition, directly affecting the solvation of PEO. Small angle neutron scattering (SANS) is used to explore the conformation of 38 kDa PEO dissolved in the PIL propylammonium nitrate (PAN), a mol fraction of 10% propylammonium chloride (PACl) in PAN, and a mole fraction of 10% propylammonium bromide (PABr) in PAN. Each of these solutions are shown to behave as a good solvent for PEO, as determined by their Flory exponents and Zimm plot analysis. The quality of solvation is reduced by the addition of the halide salt, with the order of solvation as follows: PAN > Br
Self-Consistent-Charge Density-Functional Tight-Binding/MD Simulation of Transition Metal Catalyst Particle Melting and Carbide Formation
Publisher: American Scientific Publishers
Date: 09-2011
The influence of hydrogen on transition metal - Catalysed graphene nucleation
Publisher: Elsevier BV
Date: 03-2018
Nanostructure of [Li(G4)] TFSI and [Li(G4)] NO3solvate ionic liquids at HOPG and Au(111) electrode interfaces as a function of potential
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C4CP04522J
Abstract: Atomic force microscopy (AFM) force measurements have been used to study the solvate ionic liquid (IL) double layer nanostructure at highly ordered pyrolytic graphite (HOPG) and Au(111) electrode surfaces as a function of potential.
Temperature Dependence of Catalyst-Free Chirality-Controlled Single-Walled Carbon Nanotube Growth from Organic Templates
Publisher: American Chemical Society (ACS)
Date: 09-09-2013
DOI: 10.1021/JZ4015647
Boron Nitride Nucleation Mechanism during Chemical Vapor Deposition
Publisher: American Chemical Society (ACS)
Date: 26-09-2018
The influence of magnetic moment on carbon nanotube nucleation
Publisher: Elsevier BV
Date: 08-2016
Lewis Strength Determines Specific-Ion Effects in Aqueous and Nonaqueous Solvents
Publisher: American Chemical Society (ACS)
Date: 21-06-2019
Abstract: An analysis of specific-ion effects in aqueous and nonaqueous solvents using energy decomposition analysis is presented. Specific-ion effects induce or influence physicochemical phenomena in a way that is determined by the identity of the ions present, and not merely by their charge or concentration. Such effects have been known since the seminal work of Hofmeister and are often categorized according to the well-known Hofmeister series. Ex les of specific-ion effects are ubiquitous throughout chemistry and biology and are traditionally explained in terms of the influence ions have on the structure of water. However, this explanation is unsatisfactory because it is unable to adequately explain and predict frequently observed series reversals and anomalies. Further, recent experiments have shown that specific-ion effects are observed in nonaqueous solvents. By modeling solvated ion-
Ab initiorovibrational spectra of ,BeHD2+and
Publisher: Informa UK Limited
Date: 10-10-2007
Chiral‐selective etching effects on carbon nanotube growth at edge carbon atoms
Publisher: Wiley
Date: 12-12-2019
DOI: 10.1002/JCC.25610
Abstract: Chemical vapor deposition (CVD) utilizing metal cluster nanoparticle catalysts is commonly used to synthesize carbon nanotubes (CNT), with oxygen-containing species such as water or alcohol included in the feedstock for enhanced yield. However, the etching effect of these additives on the growth mechanism has rarely been investigated, despite evidence suggesting that etching potentially affects the chirality distribution of product CNTs. We used quantum chemical methods to study how water-based etchant radicals (OH and H) may enhance the chiral selectivity during CVD growth using CNT cap models. Chemical reactivities of the caps with the etchant radicals were evaluated using density functional theory (DFT). It was found that the reactivities on the cap edges correlate with the chirality of the caps. These results suggest that proper selection of etchant species can provide opportunities for selective chirality control of the product CNTs. © 2018 Wiley Periodicals, Inc.
Group and Period-Based Representations for Improved Machine Learning Prediction of Heterogeneous Alloy Catalysts
Publisher: American Chemical Society (ACS)
Date: 25-05-2021
Ab initio vibrational spectrum of (
Publisher: Elsevier BV
Date: 2009
NO2 Solvation Structure in Choline Chloride Deep Eutectic Solvents—The Role of the Hydrogen Bond Donor
Publisher: American Chemical Society (ACS)
Date: 22-03-2018
Abstract: Deep eutectic solvents (DESs) are promising candidates as alternate media for industrial gas sequestration processes, such as denitrification via NO
The electrostatic origins of specific ion effects: quantifying the Hofmeister series for anions
Publisher: Royal Society of Chemistry (RSC)
Date: 2021
DOI: 10.1039/D1SC03568A
Abstract: Analysis of ions’ radial charge densities reveals they correlate with many specific ion effects, and provides a new basis to explain and quantify the 130-year-old Hofmeister series for anions.
Quantum chemical investigation of epoxide and ether groups in graphene oxide and their vibrational spectra
Publisher: Royal Society of Chemistry (RSC)
Date: 2013
DOI: 10.1039/C3CP00094J
Abstract: We present a detailed analysis of the factors influencing the formation of epoxide and ether groups in graphene nanoflakes using conventional density functional theory (DFT), the density-functional tight-binding (DFTB) method, π-Hückel theory, and graph theoretical invariants. The relative thermodynamic stability associated with the chemisorption of oxygen atoms at various positions on hexagonal graphene flakes (HGFs) of D(6h)-symmetry is determined by two factors - viz. the disruption of the π-conjugation of the HGF and the geometrical deformation of the HGF structure. The thermodynamically most stable structure is achieved when the former factor is minimized, and the latter factor is simultaneously maximized. Infrared (IR) spectra computed using DFT and DFTB reveal a close correlation between the relative thermodynamic stabilities of the oxidized HGF structures and their IR spectral activities. The most stable oxidized structures exhibit significant IR activity between 600 and 1800 cm(-1), whereas less stable oxidized structures exhibit little to no activity in this region. In contrast, Raman spectra are found to be less informative in this respect.
Why Carbon Nanotubes Grow
Publisher: American Chemical Society (ACS)
Date: 17-03-2022
DOI: 10.1021/JACS.2C00879
Abstract: Despite three decades of intense research efforts, the most fundamental question "why do carbon nanotubes grow?" remains unanswered. In fact, carbon nanotubes (CNTs) should not grow since the encapsulation of a catalyst with graphitic carbon is energetically more favorable than CNT growth in every aspect. Here, we answer this question using a theoretical model based on extensive first-principles and molecular dynamics calculations. We reveal a historically overlooked yet fundamental aspect of the CNT-catalyst interface, viz., that the interfacial energy of the CNT-catalyst edge is contact angle-dependent. The contact angle increases via graphitic cap lift-off, drastically decreasing the interfacial formation energy by up to 6-9 eV/nm, overcoming van der Waals cap-catalyst adhesion, and driving CNT growth. Mapping this remarkable and simple interplay allows us to understand, for the first time, why CNTs grow.
Trends in low-lying electronic states of XH2 (X=Li, Na, K)
Publisher: Elsevier BV
Date: 03-2008
Theoretical Insights into Chirality‐Controlled SWCNT Growth from a Cycloparaphenylene Template
Publisher: Wiley
Date: 05-03-2012
Abstract: A self-assembly mechanism for low-temperature SWCNT growth from a [6]cycloparaphenylene ([6]CPP) precursor via ethynyl (C(2)H) radical addition is presented, based on non-equilibrium quantum chemical molecular dynamics (QM/MD) simulations and density functional theory (DFT) calculations. This mechanism, which maintains the (6,6) armchair chirality of a SWCNT fragment throughout the growth process, is energetically more favorable than a previously proposed Diels-Alder-based growth mechanisms [E. H. Fort, et al., J. Mater. Chem. 2011, 21, 1373]. QM/MD simulations and DFT calculations show that C(2)H radicals play dual roles during SWCNT growth, by abstracting hydrogen from the SWCNT fragment and providing the carbon source necessary for growth itself. Simulations demonstrate that chirality-controlled SWCNT growth from macrocyclic hydrocarbon seed molecules with pre-selected edge structure can be accomplished when the reaction conditions are carefully selected for hydrogen abstraction by radical species during the growth process.
Inducing regioselective chemical reactivity in graphene with alkali metal intercalation
Publisher: Royal Society of Chemistry (RSC)
Date: 2018
DOI: 10.1039/C8CP02903B
Abstract: Intercalating alkali metal atoms between metal substrates and adsorbed graphene monolayers yields curvature-induced regioselective reactivity of graphene.
Discovery of Graphene Growth Alloy Catalysts Using High-Throughput Machine Learning
Publisher: American Chemical Society (ACS)
Date: 27-10-2023
3-Dimensional atomic scale structure of the ionic liquid–graphite interface elucidated by AM-AFM and quantum chemical simulations
Publisher: Royal Society of Chemistry (RSC)
Date: 2014
DOI: 10.1039/C4NR01219D
Abstract: In situ litude modulated atomic force microscopy (AM-AFM) and quantum chemical simulations are used to resolve the structure of the highly ordered pyrolytic graphite (HOPG)-bulk propylammonium nitrate (PAN) interface with resolution comparable with that achieved for frozen ionic liquid (IL) monolayers using STM. This is the first time that (a) molecular resolution images of bulk IL-solid interfaces have been achieved, (b) the lateral structure of the IL graphite interface has been imaged for any IL, (c) AM-AFM has elucidated molecular level structure immersed in a viscous liquid and (d) it has been demonstrated that the IL structure at solid surfaces is a consequence of both thermodynamic and kinetic effects. The lateral structure of the PAN-graphite interface is highly ordered and consists of remarkably well-defined domains of a rhomboidal superstructure composed of propylammonium cations preferentially aligned along two of the three directions in the underlying graphite lattice. The nanostructure is primarily determined by the cation. Van der Waals interactions between the propylammonium chains and the surface mean that the cation is enriched in the surface layer, and is much less mobile than the anion. The presence of a heterogeneous lateral structure at an ionic liquid-solid interface has wide ranging ramifications for ionic liquid applications, including lubrication, capacitive charge storage and electrodeposition.
Combined friction force microscopy and quantum chemical investigation of the tribotronic response at the propylammonium nitrate–graphite interface
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C5CP01952D
Abstract: The energetic origins of the variation in friction with potential at the propylammonium nitrate–graphite interface are revealed using friction force microscopy (FFM) in combination with quantum chemical simulations.
Decomposing Hofmeister effects on amino acid residues with symmetry adapted perturbation theory
Publisher: IOP Publishing
Date: 03-2023
Abstract: Hofmeister effects, and more generally specific ion effects, are observed broadly in biological systems. However, there are many cases where the Hofmeister series might not be followed in complex biological systems, such as ion channels which can be highly specific to a particular ion. An understanding of how ions from the Hofmeister series interact with the proteinogenic amino acids will assist elucidation of why some binding interactions may be favoured over others. Using symmetry adapted perturbation theory (SAPT2 + 3), the interaction energies between a selection of anions and each amino acid have been investigated. The interaction strengths become more favourable in accordance with the Hofmeister series, and also with increasing polarity of the amino acids (with the exception of the negatively charged amino acid side chains). Furthermore, the interactions are generally most favourable when they simultaneously involve the side chain and both protic moieties of the backbone. The total interaction energy in these anion–amino acid complexes is also primarily determined by its electrostatic component, in a manner proportional to the þ (‘sho’) value of the anion.
Density functional tight binding-based free energy simulations in the DFTB+ program
Publisher: Wiley
Date: 20-09-2018
DOI: 10.1002/JCC.25583
Abstract: The timescale problem-in which high barriers on the free energy surface trap molecular dynamics simulations in local energy wells-is a key limitation of current reactive MD simulations based on the density functional tight binding (DFTB) potential. Here, we report a new interface between the DFTB+ software package and the PLUMED library for performing DFTB-based free energy calculations. We demonstrate the performance of this interface for 3 archetypal rare-event chemical reactions, (i) intramolecular proton transfer in malonaldehyde, (ii) bowl inversion in corannulene, and (iii) oxygen diffusion on graphene. Using third-order DFTB in conjunction with metadynamics (with/without multiple walkers) and well-tempered metadynamics, we report here free energies of activation (ΔG
Selective cytotoxicity of organotin(IV) compounds with 2,3-dihydroxybenzyldithiocarbazate Schiff bases
Publisher: Springer Science and Business Media LLC
Date: 05-02-2020
Accurate Thermochemical and Kinetic Stabilities of C84 Isomers
Publisher: American Chemical Society (ACS)
Date: 24-04-2018
Abstract: Accurate double-hybrid density functional theory and isodesmic-type reaction schemes are utilized to report accurate estimates of the heats of formation (Δ
Atomistic Mechanism of Carbon Nanostructure Self-Assembly as Predicted by Nonequilibrium QM/MD Simulations
Publisher: Springer Netherlands
Date: 2012
A global reaction route mapping-based kinetic Monte Carlo algorithm
Publisher: AIP Publishing
Date: 12-07-2016
DOI: 10.1063/1.4954660
Abstract: We propose a new on-the-fly kinetic Monte Carlo (KMC) method that is based on exhaustive potential energy surface searching carried out with the global reaction route mapping (GRRM) algorithm. Starting from any given equilibrium state, this GRRM-KMC algorithm performs a one-step GRRM search to identify all surrounding transition states. Intrinsic reaction coordinate pathways are then calculated to identify potential subsequent equilibrium states. Harmonic transition state theory is used to calculate rate constants for all potential pathways, before a standard KMC accept/reject selection is performed. The selected pathway is then used to propagate the system forward in time, which is calculated on the basis of 1st order kinetics. The GRRM-KMC algorithm is validated here in two challenging contexts: intramolecular proton transfer in malonaldehyde and surface carbon diffusion on an iron nanoparticle. We demonstrate that in both cases the GRRM-KMC method is capable of reproducing the 1st order kinetics observed during independent quantum chemical molecular dynamics simulations using the density-functional tight-binding potential.
Reaction pathways in the solid state and the Hubbard U correction
Publisher: AIP Publishing
Date: 26-03-2021
DOI: 10.1063/5.0045526
Abstract: We investigate how the Hubbard U correction influences vacancy defect migration barriers in transition metal oxide semiconductors. We show that, depending on the occupation of the transition metal d orbitals, the Hubbard U correction can cause severe instabilities in the migration barrier energies predicted using generalized gradient approximation density functional theory (GGA DFT). For the d0 oxide SrTiO3, applying a Hubbard correction to the Ti4+ 3d orbitals below 4–5 eV yields a migration barrier of ∼0.4 eV. However, above this threshold, the barrier increases suddenly to ∼2 eV. This sudden increase in the transition state barrier arises from the Hubbard U correction changing the Ti4+ t2g/eg orbital occupation, and hence electron density localization, along the migration pathway. Similar results are observed in the d10 oxide ZnO however, significantly larger Hubbard U corrections must be applied to the Zn2+ 3d orbitals for the same instability to be observed. These results highlight important limitations to the application of the Hubbard U correction when modeling reactive pathways in solid state materials using GGA DFT.
Thermochemical stabilities of giant fullerenes using density functional tight binding theory and isodesmic‐type reactions
Publisher: Wiley
Date: 20-11-2020
DOI: 10.1002/JCC.26449
Abstract: We present a systematic assessment of the density functional tight binding (DFTB) method for calculating heats of formation of fullerenes with isodesmic‐type reaction schemes. We show that DFTB3‐D/3ob can accurately predict Δ f H values of the 1812 structural isomers of C 60 , reproduce subtle trends in Δ f H values for 24 isolated pentagon rule (IPR) isomers of C 84 , and predict Δ f H values of giant fullerenes that are in effectively exact agreement with benchmark DSD‐PBEP86/def2‐QZVPP calculations. For fullerenes up to C 320 , DFTB Δ f H values are within 1.0 kJ mol −1 of DSD‐PBEP86/def2‐QZVPP values per carbon atom, and on a per carbon atom basis DFTB3‐D/3ob yields exactly the same numerical trend of (Δ f H [per carbon] = 722 n −0.72 + 5.2 kJ mol −1 ). DFTB3‐D/3ob is therefore an accurate replacement for high‐level DHDFT and composite thermochemical methods in predicting of thermochemical stabilities of giant fullerenes and analogous nanocarbon architectures.
Electronic Structure and High-Temperature Thermochemistry of Oxygen-Deficient BaMO3 (M = Ti – Cu) Perovskites
Publisher: American Chemical Society (ACS)
Date: 23-11-2020
Milestones in molecular dynamics simulations of single-walled carbon nanotube formation: A brief critical review
Publisher: Springer Science and Business Media LLC
Date: 10-2009
Boron Nitride Nanotube Nucleation during Ni-Catalyzed Boron Oxide Chemical Vapor Deposition
Publisher: American Chemical Society (ACS)
Date: 12-10-2019
Density functional theory modeling of critical properties of perovskite oxides for water splitting applications
Publisher: Wiley
Date: 08-05-2023
DOI: 10.1002/WENE.476
Abstract: Water splitting (WS) driven by solar energy is considered as a promising strategy to produce renewable hydrogen from water with minimal environmental impact. Realization of large‐scale hydrogen production by this approach requires cost‐effective, efficient and stable materials to drive the WS reaction. Perovskite oxides have recently attracted widespread attention in WS applications due to their unique structural features, such as compositional and structural flexibility allowing them to achieve desired sunlight absorption capability, precise control of electrocatalytic and redox activity to drive the chemical reaction, tuneable bandgaps and band edges, and earth‐abundance. However, perovskite oxides contain a large family of metal oxides and experimental exploration of novel perovskites without a priori knowledge of their properties could be costly and time‐consuming. First‐principles approaches such as density functional theory (DFT) are a useful and cost‐effective alternative towards this end. In this review, DFT‐based calculations for accurate prediction of the critical properties of ABO 3 perovskite oxides relevant to WS processes are surveyed. Structural, electronic, optical, surface, and thermal properties are grouped according to their relevance to photocatalytic (PC), electrochemical (EC), photo‐electrochemical (PEC), and solar thermal water splitting (STWS) processes. The challenges associated with the choice of exchange‐correlation (XC) functional in DFT methods for precise prediction of these properties are discussed and specific XC functionals have been recommended where experimental comparisons are possible. This article is categorized under: Sustainable Energy Solar Energy Emerging Technologies Hydrogen and Fuel Cells Emerging Technologies Materials
Dithiocarbazate Ligand-Based Cu(II), Ni(II), and Zn(II) Complexes: Synthesis, Structural Investigations, Cytotoxicity, DNA Binding, and Molecular Docking Studies
Publisher: Hindawi Limited
Date: 31-07-2022
DOI: 10.1155/2022/2004052
Abstract: S-4-methylbenzyl-β-N-(2-methoxybenzylmethylene)dithiocarbazate ligand, 1, prepared from S-(4-methylbenzyl)dithiocarbazate, was used to produce a novel series of transition metal complexes of the type, [M (L)2] [M = Cu(II) (2), Ni(II) (3), and Zn(II) (4), L = 1]. The ligand and its complexes were investigated by elemental analysis, FTIR, 1H and 13C-NMR, MS spectrometry, and molar conductivity. In addition, single X-ray crystallography was also performed for ligand, 1, and complex 3. The Hirshfeld surface analyses were also performed to know about various bonding interactions in the ligand, 1, and complex 3. The investigated compounds were also tested to evaluate their cytotoxic behaviour. However, complex 2 showed promising results against MCF-7 and MDA-MB-213 cancer cell lines. Furthermore, the interaction of CT-DNA with ligand, 1, and complex 2 was also studied using the electronic absorption method, revealing that the compounds have potential DNA-binding ability via hydrogen bonding and hydrophobic and van der Waals interactions. A molecular docking study of complex 2 was also carried out, which revealed that free binding free energy value was −7.39 kcal mol−1.
Graphene Nucleation from Amorphous Nickel Carbides: QM/MD Studies on the Role of Subsurface Carbon Density
Publisher: American Chemical Society (ACS)
Date: 08-05-2014
DOI: 10.1021/JP4123612
Nearly Exclusive Growth of Small Diameter Semiconducting Single-Wall Carbon Nanotubes from Organic Chemistry Synthetic End-Cap Molecules
Publisher: American Chemical Society (ACS)
Date: 18-12-2014
DOI: 10.1021/NL504066F
Abstract: The inability to synthesize single-wall carbon nanotubes (SWCNTs) possessing uniform electronic properties and chirality represents the major impediment to their widespread applications. Recently, there is growing interest to explore and synthesize well-defined carbon nanostructures, including fullerenes, short nanotubes, and sidewalls of nanotubes, aiming for controlled synthesis of SWCNTs. One noticeable advantage of such processes is that no metal catalysts are used, and the produced nanotubes will be free of metal contamination. Many of these methods, however, suffer shortcomings of either low yield or poor controllability of nanotube uniformity. Here, we report a brand new approach to achieve high-efficiency metal-free growth of nearly pure SWCNT semiconductors, as supported by extensive spectroscopic characterization, electrical transport measurements, and density functional theory calculations. Our strategy combines bottom-up organic chemistry synthesis with vapor phase epitaxy elongation. We identify a strong correlation between the electronic properties of SWCNTs and their diameters in nanotube growth. This study not only provides material platforms for electronic applications of semiconducting SWCNTs but also contributes to fundamental understanding of the growth mechanism and controlled synthesis of SWCNTs.
New Phosphorene by Phase Combination with Tunable Electronic and Mechanical Properties
Publisher: American Chemical Society (ACS)
Date: 10-04-2019
Assessment of the Density Functional Tight Binding Method for Protic Ionic Liquids
Publisher: American Chemical Society (ACS)
Date: 11-09-2014
DOI: 10.1021/CT500394T
Tin(IV) compounds of tridentate thiosemicarbazone Schiff bases: Synthesis, characterization, in-silico analysis and in vitro cytotoxicity
Publisher: Elsevier BV
Date: 10-2020
Carbon Coating Precedes SWCNT Nucleation on Silicon Nanoparticles: Insights from QM/MD Simulations
Publisher: American Chemical Society (ACS)
Date: 14-02-2013
DOI: 10.1021/JP3098999
Chiral-Selective Carbon Nanotube Etching with Ammonia: A Quantum Chemical Investigation
Publisher: American Chemical Society (ACS)
Date: 24-08-2016
Spanning the “Parameter Space” of Chemical Vapor Deposition Graphene Growth with Quantum Chemical Simulations
Publisher: American Chemical Society (ACS)
Date: 26-05-2016
Optimization of a Genetic Algorithm for the Functionalization of Fullerenes
Publisher: American Chemical Society (ACS)
Date: 24-04-2012
DOI: 10.1021/CT300190U
Abstract: We present the optimization of a genetic algorithm (GA) that is designed to predict the most stable structural isomers of hydrogenated and hydroxylated fullerene cages. Density functional theory (DFT) and density functional tight binding (DFTB) methods are both employed to compute isomer energies. We show that DFTB and DFT levels of theory are in good agreement with each other and that therefore both sets of optimized GA parameters are very similar. As a prototypical fullerene cage, we consider the functionalization of the C20 species, since for this smallest possible fullerene cage it is possible to compute all possible isomer energies for evaluation of the GA performance. An energy decomposition analysis for both C20Hn and C20(OH)n systems reveals that, for only few functional groups, the relative stabilities of different structural isomers may be rationalized simply with recourse to π-Hückel theory. However, upon a greater degree of functionalization, π-electronic effects alone are incapable of describing the interaction between the functional groups and the distorted cage, and both σ- and π-electronic structure must be taken into account in order to understand the relative isomer stabilities.
A quantum chemical molecular dynamics repository of solvated ions
Publisher: Springer Science and Business Media LLC
Date: 21-07-2022
DOI: 10.1038/S41597-022-01527-8
Abstract: The importance of ion-solvent interactions in predicting specific ion effects in contexts ranging from viral activity through to electrolyte viscosity cannot be underestimated. Moreover, investigations of specific ion effects in nonaqueous systems, highly relevant to battery technologies, biochemical systems and colloid science, are severely limited by data deficiency. Here, we report IonSolvR – a collection of more than 3,000 distinct nanosecond-scale ab initio molecular dynamics simulations of ions in aqueous and non-aqueous solvent environments at varying effective concentrations. Density functional tight binding (DFTB) is used to detail the solvation structure of up to 55 solutes in 28 different protic and aprotic solvents. DFTB is a fast quantum chemical method, and as such enables us to bridge the gap between efficient computational scaling and maintaining accuracy, while using an internally-consistent simulation technique. We validate the database against experimental data and provide guidance for accessing in idual IonSolvR records.
General H2 Activation Modes for Lewis Acid–Transition Metal Bifunctional Catalysts
Publisher: American Chemical Society (ACS)
Date: 08-02-2016
Trends in MH2 n+ ion-quadrupole complexes (M = Li, Be, Na, Mg, K, Ca; N = 1, 2) using ab initio methods
Publisher: Royal Society of Chemistry (RSC)
Date: 2010
DOI: 10.1039/C0CP00498G
Abstract: The ground state potential energy surfaces (PESs) of MH(2)(n+) (M = Li, Be, Na, Mg, K, Ca n = 1, 2) have been investigated using relativistically corrected, coupled-cluster (CC) and multi-reference configuration interaction (MRCI) methods. The PESs for MH(2)(+) (M = Li, Na, K) and MH(2)(n+) (M = Be, Mg, Ca n = 1, 2) exhibit global minima corresponding to C(2v) symmetry equilibrium structures, with local minima for D(∞h) and C(∞v) symmetry states. Conversely, the ground state PESs of LiH(2)(2+), NaH(2)(2+) and KH(2)(2+) are repulsive. In all cases, the D(∞h) states resulting from the insertion of M(n+) into the H(2) moiety were significantly higher in energy than the co-linear C(2v) states. It is generally assumed a priori that these species are the result of the interaction between the metal ion charge state and the quadrupole moment of the H(2) moiety. However, analysis of the functional ΔΘ(αα)(R(M(n+)-H(2))) = Θ(αα)(MH(2)(n+)) - Θ(αα)(M(n+)) (which is effectively the difference between traceless quadrupole moments (Θ(αα)) of MH(2)(n+) and the isolated M(n+) ion computed using MRCI) as a function of M(n+)-H(2) distance demonstrates that a local maximum in ΔΘ(αα) along the molecular C(2) axis is necessary for the formation of a thermodynamically stable complex. It is concluded that the topology of ΔΘ(αα) provides a convenient indicator of the stability of such molecular ion-quadrupole complexes.
Nanostructure of propylammonium nitrate in the presence of poly(ethylene oxide) and halide salts
Publisher: AIP Publishing
Date: 16-02-2018
DOI: 10.1063/1.5012801
Abstract: Nanoscale structure of protic ionic liquids is critical to their utility as molecular electrochemical solvents since it determines the capacity to dissolve salts and polymers such as poly(ethylene oxide) (PEO). Here we use quantum chemical molecular dynamics simulations to investigate the impact of dissolved halide anions on the nanostructure of an archetypal nanostructured protic ionic liquid, propylammonium nitrate (PAN), and how this impacts the solvation of a model PEO polymer. At the molecular level, PAN is nanostructured, consisting of charged olar and uncharged/nonpolar domains. The charged domain consists of the cation/anion charge groups, and is formed by their electrostatic interaction. This domain solvophobically excludes the propyl chains on the cation, which form a distinct, self-assembled nonpolar domain within the liquid. Our simulations demonstrate that the addition of Cl− and Br− anions to PAN disrupts the structure within the PAN charged domain due to competition between nitrate and halide anions for the ammonium charge centre. This disruption increases with halide concentration (up to 10 mol. %). However, at these concentrations, halide addition has little effect on the structure of the PAN nonpolar domain. Addition of PEO to pure PAN also disrupts the structure within the charged domain of the liquid due to hydrogen bonding between the charge groups and the terminal PEO hydroxyl groups. There is little other association between the PEO structure and the surrounding ionic liquid solvent, with strong PEO self-interaction yielding a compact, coiled polymer morphology. Halide addition results in greater association between the ionic liquid charge centres and the ethylene oxide components of the PEO structure, resulting in reduced conformational flexibility, compared to that observed in pure PAN. Similarly, PEO self-interactions increase in the presence of Cl− and Br− anions, compared to PAN, indicating that the addition of halide salts to PAN decreases its utility as a molecular solvent for polymers such as PEO.
Formation of chlorobenzenes by oxidative thermal decomposition of 1,3-dichloropropene
Publisher: Elsevier BV
Date: 06-2015
Sub-surface nucleation of graphene precursors near a Ni(111) step-edge
Publisher: Royal Society of Chemistry (RSC)
Date: 2012
DOI: 10.1039/C2CC32995F
Abstract: Graphene nucleation on Ni(111) has been modeled using QM/MD simulations. We demonstrate that graphene precursor nucleation can occur underneath the catalyst surface. In addition, a Ni(111) step-edge is not a static structure, as is often assumed it is instead highly malleable, being deformed and subsequently healed during graphene nucleation.
Defect Engineering for Photocatalysis: From Ternary to Perovskite Oxynitrides
Publisher: Wiley
Date: 06-02-2020
Thermal annealing of SiC nanoparticles induces SWNT nucleation: evidence for a catalyst-independent VSS mechanism
Publisher: Royal Society of Chemistry (RSC)
Date: 2011
DOI: 10.1039/C1CP21236B
Abstract: Density-functional tight-binding molecular dynamics (DFTB/MD) methods were employed to demonstrate single-walled carbon nanotube (SWNT) nucleation resulting from thermal annealing of SiC nanoparticles. SWNT nucleation in this case is preceded by a change of the SiC structure from a crystalline one, to one in which silicon and carbon are segregated. This structural transformation ultimately resulted in the formation of extended polyyne chains on the SiC nanoparticle surface. These polyyne chains subsequently coalesced, forming an extended sp(2)-hybridized carbon cap on the SiC nanoparticle. The kinetics of this process were enhanced significantly at higher temperatures (2500 K), compared to lower temperatures (1200 K) and so directly correlated to the surface premelting behavior of the nanoparticle structure. Analysis of the SiC nanoparticle Lindemann index between 1000 and 3000 K indicated that SWNT nucleation at temperatures below 2600 K occurred in the solid, or quasi-solid, phase. Thus, the traditional vapor-liquid-solid mechanism of SWNT growth does not apply in the case of SiC nanoparticles. Instead, we propose that this ex le of SWNT nucleation constitutes evidence of a vapor-solid-solid process. This conclusion complements our recent observations regarding SWNT nucleation on SiO(2) nanoparticles (A. J. Page, K. R. S. Chandrakumar, S. Irle and K. Morokuma, J. Am. Chem. Soc., 2011, 133, 621-628). In addition, similarities between the atomistic SWNT nucleation mechanisms on SiC and SiO(2) catalysts provide the first evidence of a catalyst-independent SWNT nucleation mechanism with respect to 'non-traditional' SWNT catalyst species.
Ab initio properties and potential energy surface of the ground electronic state of BeHe2 +
Publisher: Elsevier BV
Date: 09-2006
Quantum Chemical Molecular Dynamics Simulation of Single-Walled Carbon Nanotube Cap Nucleation on an Iron Particle
Publisher: American Chemical Society (ACS)
Date: 14-10-2009
DOI: 10.1021/NN900784F
Abstract: The atomic scale details of single-walled carbon nanotube (SWNT) nucleation on metal catalyst particles are elusive to experimental observations. Computer simulation of metal-catalyzed SWNT nucleation is a challenging topic but potentially of great importance to understand the factors affecting SWNT diameters, chirality, and growth efficiency. In this work, we use nonequilibrium density functional tight-binding molecular dynamics simulations and report nucleation of sp(2)-carbon cap structures on an iron particle consisting of 38 atoms. One C(2) molecule was placed every 1.0 ps around an Fe(38) cluster for 30 ps, after which a further 410 ps of annealing simulation without carbon supply was performed. We find that sp(2)-carbon network nucleation and annealing processes occur in three sequential and repetitive stages: (A) polyyne chains on the metal surface react with each other to evolve into a Y-shaped polyyne junction, which preferentially form a five-membered ring as a nucleus (B) polyyne chains on the first five-membered ring form an additional fused five- or six-membered ring and (C) pentagon-to-hexagon self-healing rearrangement takes place with the help of short-lived polyyne chains, stabilized by the mobile metal atoms. The observed nucleation process resembles the formation of a fullerene cage. However, the metal particle plays a key role in differentiating the nucleation process from fullerene cage formation, most importantly by keeping the growing cap structure from closing into a fullerene cage and by keeping the carbon edge "alive" for the addition of new carbon material.
Experimental, computational and thermodynamic studies in perovskites metal oxides for thermochemical fuel production: A review
Publisher: Elsevier BV
Date: 04-2020
Mechanisms of Single-Walled Carbon Nanotube Nucleation, Growth and Chirality-Control: Insights from QM/MD Simulations
Publisher: InTech
Date: 27-07-2011
DOI: 10.5772/17725
Quantum Chemical Molecular Dynamics Simulations of 1,3-Dichloropropene Combustion
Publisher: American Chemical Society (ACS)
Date: 19-08-2015
Abstract: Oxidative decomposition of 1,3-dichloropropene was investigated using quantum chemical molecular dynamics (QM/MD) at 1500 and 3000 K. Thermal oxidation of 1,3-dichloropropene was initiated by (1) abstraction of allylic H/Cl by O2 and (2) intra-annular C-Cl bond scission and elimination of allylic Cl. A kinetic analysis shows that (2) is the more dominant initiation pathway, in agreement with QM/MD results. These QM/MD simulations reveal new routes to the formation of major products (H2O, CO, HCl, CO2), which are propagated primarily by the chloroperoxy (ClO2), OH, and 1,3-dichloropropene derived radicals. In particular, intra-annular C-C/C-H bond dissociation reactions of intermediate aldehydes/ketones are shown to play a dominant role in the formation of CO and CO2. Our simulations demonstrate that both combustion temperature and radical concentration can influence the product yield, however not the combustion mechanism.
Initial competing chemical pathways during floating catalyst chemical vapor deposition carbon nanotube growth
Publisher: AIP Publishing
Date: 22-01-2021
DOI: 10.1063/5.0030814
Abstract: Ferrocene (Fc) is an effective precursor for the direct synthesis of high quality single-walled carbon nanotubes (SWCNTs) via floating catalyst chemical vapor deposition (FCCVD). However, the formation mechanism of the Fe floating catalyst and the SWNCT growth precursors, such as carbon chains, during Fc decomposition are not well understood. Here, we report first principles nonequilibrium quantum chemical molecular dynamics simulations that investigate the decomposition of Fc during FCCVD. We examine the influence of additional growth precursors including ethylene, methane, CO, and CO2 on the Fc decomposition mechanism and show that the dissociation of these species into C2Hx radicals and C atoms provides the key growth agents for the nucleation of carbon chains from Fc-derived species such as cyclopentadienyl rings. Without an additional growth precursor, Fc decomposes via the spontaneous cleavage of Fe–C and C–H bonds, thereby enabling Fe atoms to cluster and form the floating catalyst. On the basis of these simulations, we detail the two competing chemical pathways present during the initial stages of FCCVD: Fe catalyst nanoparticle growth and carbon chain growth. The latter is accelerated in the presence of the additional growth precursors, with the identity of the precursor determining the nature of the balance between these competing pathways.
Mechanisms of Single-Walled Carbon Nanotube Nucleation, Growth, and Healing Determined Using QM/MD Methods
Publisher: American Chemical Society (ACS)
Date: 27-07-2010
DOI: 10.1021/AR100064G
Abstract: Since their discovery in the early 1990s, single-walled carbon nanotubes (SWNTs) have spawned previously unimaginable commercial and industrial technologies. Their versatility stems from their unique electronic, physical/chemical, and mechanical properties, which set them apart from traditional materials. Many researchers have investigated SWNT growth mechanisms in the years since their discovery. The most prevalent of these is the vapor-liquid-solid (VLS) mechanism, which is based on experimental observations. Within the VLS mechanism, researchers assume that the formation of a SWNT starts with co-condensation of carbon and metal atoms from vapor to form liquid metal carbide. Once the liquid reaches supersaturation, the solid phase nanotubes begin to grow. The growth process is partitioned into three distinct stages: nucleation of a carbon "cap-precursor," "cap-to-tube" transformation, and continued SWNT growth. In recent years, molecular dynamics (MD) simulations have come to the fore with respect to SWNT growth. MD simulations lead to spatial and temporal resolutions of these processes that are superior to those possible using current experimental techniques, and so provide valuable information regarding the growth process that researchers cannot obtain experimentally. In this Account, we review our own recent efforts to simulate SWNT nucleation, growth, and healing phenomena on transition-metal catalysts using quantum mechanical molecular dynamics (QM/MD) methods. In particular, we have validated each stage of the SWNT condensation mechanism using a self-consistent-charge density-functional tight-binding (SCC-DFTB) methodology. With respect to the nucleation of a SWNT cap-precursor (stage 1), we have shown that the presence of a transition-metal carbide particle is not a necessary prerequisite for SWNT nucleation, contrary to conventional experimental presumptions. The formation and coalescence of polyyne chains on the metal surface occur first, followed by the formation of the SWNT cap-precursor, "ring condensation", and the creation of an sp(2)-hybridized carbon structure. In our simulations, the nucleation process takes approximately 400 ps. This first step occurs over a much longer time scale than the second stage of SWNT condensation (approximately 50 ps). We therefore observe SWNT nucleation to be akin to the rate-limiting step of the SWNT formation process. In addition to the QM/MD simulation of various stages of SWNT nucleation, growth, and healing processes, we have determined the effects of temperature, catalyst composition, and catalyst size on the kinetics and mechanism of SWNT growth. With respect to temperature dependence, we observe a "sweet-spot" with respect to the efficiency of SWNT growth. In addition, Ni-catalyzed SWNT growth is observed to be 70-100% faster compared to Fe-catalyzed SWNT growth, depending on the catalyst particle size. We also observe a noticeable increase in SWNT growth rates using smaller catalyst particles. Finally, we review our recent QM/MD investigation of SWNT healing. In particular, we recount mechanisms by which adatom defects, monovacancy defects, and a "5-7 defect" are removed from a nascent SWNT. The effectiveness of these healing mechanisms depends on the rate at which carbon moieties are incorporated into the growing SWNT. Explicitly, we observe that healing is promoted using a slower carbon supply rate. From this rudimentary control of SWNT healing, we propose a route towards chirality-controlled SWNT growth.
First-principles thermochemical properties of hexagonal and cubic phase BaMnO3
Publisher: Elsevier BV
Date: 06-2022
Effects of Molecular Dynamics Thermostats on Descriptions of Chemical Nonequilibrium
Publisher: American Chemical Society (ACS)
Date: 17-10-2012
DOI: 10.1021/CT3004639
Abstract: The performance of popular molecular dynamics (MD) thermostat algorithms in constant temperature simulations of equilibrium systems is well-known. This is not the case, however, in the context of nonequilibrium chemical systems, such as chemical reactions or nanoscale self-assembly processes. In this work, we investigate the effect of popular thermostat algorithms on the "natural" (i.e., Hamiltonian) dynamics of a nonequilibrium, chemically reacting system. By comparing constant-temperature quantum mechanical MD (QM/MD) simulations of carbon vapor condensation using velocity scaling, Berendsen, Andersen, Langevin, and Nosé-Hoover chain thermostat algorithms with natural NVE simulations, we show that efficient temperature control and reliable reaction dynamics are mutually exclusive in such a system. This problem may be circumvented, however, by placing the reactive system in an inert He atmosphere, which is itself described using NVT MD. We demonstrate that both realistic temperature control and dynamics consistent with natural NVE dynamics can then be obtained simultaneously. In essence, the thermal energy created by the natural dynamics of the NVE subsystem is drained by the thermostat acting on the NVT atmosphere, without adversely affecting the dynamics of the reactive system itself.
Deep eutectic solvents—The vital link between ionic liquids and ionic solutions
Publisher: AIP Publishing
Date: 15-10-2021
DOI: 10.1063/5.0072268
Abstract: When selecting a solvent for a given solute, the strongly held idiom “like dissolves like”, meaning that polar solvents are used for polar solutes, is often used. This idea has resulted from the concept that most molecular solvents are homogeneous. In a deep eutectic solvent (DES), however, both components can be ionic or non-ionic, polar or non-polar. By tuning the components, DESs can solubilize a wide variety of solutes, often mixing hydrophobic and hydrophilic components, and the mixture can be designed to control phase behavior. The liquids often contain significant short-length order, and preferential solvation of one component often occurs. The addition of small polar molecules such as water or alcohols results in non-homogeneous liquids, which have significantly decreased viscosity and increased ionic conductivity. Accordingly, the areas covered in this special issue focus on structure and dynamics, solvation, the mobility of charged species, and the ability to obtain controllable phase behavior by adding polar diluents or using hydrophobic DESs.
Molecular Dynamics Simulation of the Low-Temperature Partial Oxidation of CH4
Publisher: American Chemical Society (ACS)
Date: 23-01-2009
DOI: 10.1021/JP809576K
Abstract: Low-temperature partial oxidation of methane was investigated using reactive molecular dynamics (MD) and quantum mechanical (QM) methods. In particular, the ReaxFF hydrocarbon force field [Chenoweth, K. et al. J. Phys. Chem. A 2008, 112, 1040] was employed to simulate a [20 CH(4) + 10 O(2)] model system at 500 degrees C. The chemical mechanism of the partial oxidation of methane was proposed on the basis of analysis of the computed trajectory of this model system. The partial oxidation of methane was observed to be initiated by the abstraction of hydrogen from CH(4) by O(2) and the atomization of CH(4) itself. Subsequent radical recombination between hydrogen atoms and the dehydrogenation of CH(4) were the primary pathways by which H(2) was formed. In agreement with current models of low-temperature combustion, radicals including H(3)C-OO and H(2)C-OO were also observed during the MD simulation. The observed reaction mechanism was subsequently analyzed using QM methods. For instance, structural features of prominent radical species observed during the MD simulation were analyzed using density functional theory (DFT) and coupled-cluster (CCSD(T)) methods. Enthalpies of reaction of all observed chemical processes were calculated using DFT and the W1 composite method. Where possible, comparisons with experimental data were made.
Hybrid Low‐Dimensional Carbon Allotropes Formed in Gas Phase
Publisher: Wiley
Date: 13-09-2020
Formation of benzofuran and chlorobenzofuran from 1,3-dichloropropene: A quantum chemical investigation
Publisher: Wiley
Date: 18-09-2015
DOI: 10.1002/QUA.25010
Catalyst- and Etchant-Dependent Mechanisms of Single-Walled Carbon Nanotube Nucleation during Chemical Vapor Deposition
Publisher: American Chemical Society (ACS)
Date: 14-03-2019
Homoleptic tin(IV) compounds containing tridentate ONS dithiocarbazate Schiff bases: Synthesis, X-ray crystallography, DFT and cytotoxicity studies
Publisher: Elsevier BV
Date: 04-2020
The Hubbard-U correction and optical properties of d0 metal oxide photocatalysts
Publisher: AIP Publishing
Date: 11-12-2020
DOI: 10.1063/5.0027080
Abstract: We report a systematic investigation of in idual and multisite Hubbard-U corrections for the electronic, structural, and optical properties of the metal titanate oxide d0 photocatalysts SrTiO3 and rutile/anatase TiO2. Accurate bandgaps for these materials can be reproduced with local density approximation and generalized gradient approximation exchange-correlation density functionals via a continuous series of empirically derived Ud and Up combinations, which are relatively insensitive to the choice of functional. On the other hand, lattice parameters are much more sensitive to the choice of Ud and Up, but in a systematic way that enables the Ud and Up corrections to be used to qualitatively gauge the extent of self-interaction error in the electron density. Modest Ud corrections (e.g., 4 eV–5 eV) yield the most reliable dielectric response functions for SrTiO3 and are comparable to the range of Ud values derived via linear response approaches. For r-TiO2 and a-TiO2, however, the Ud,p corrections that yield accurate bandgaps fail to accurately describe both the parallel and perpendicular components of the dielectric response function. Analysis of in idual Ud and Up corrections on the optical properties of SrTiO3 suggests that the most consequential of the two in idual corrections is Ud, as it predominately determines the accuracy of the dominant excitation from O-2p to the Ti-3d t2g/eg orbitals. Up, on the other hand, can be used to shift the entire optical response uniformly to higher frequencies. These results will assist high-throughput and machine learning approaches to screening photoactive materials based on d0 photocatalysts.
Template Effect in the Competition between Haeckelite and Graphene Growth on Ni(111): Quantum Chemical Molecular Dynamics Simulations
Publisher: American Chemical Society (ACS)
Date: 27-10-2011
DOI: 10.1021/JA2064654
Abstract: Quantum chemical molecular dynamics (QM/MD) simulations of ensembles of C(2) molecules on the Ni(111) terrace show that, in the absence of a hexagonal template or step edge, Haeckelite is preferentially nucleated over graphene as a metastable intermediate. The nucleation process is dominated by the swift transition of long carbon chains toward a fully connected sp(2) carbon network. Starting from a pentagon as nucleus, pentagons and heptagons condense during ring collapse reactions, which results in zero overall curvature. To the contrary, in the presence of a coronene-like C(24) template, hexagonal ring formation is clearly promoted, in agreement with recent suggestions from experiments. In the absence of step edges or molecular templates, graphene nucleation follows Ostwald's "rule of stages" cascade of metastable states, from linear carbon chains, via Haeckelite islands that finally anneal to graphene.
Graphene nucleation on a surface-molten copper catalyst: quantum chemical molecular dynamics simulations
Publisher: Royal Society of Chemistry (RSC)
Date: 2014
DOI: 10.1039/C4SC00491D
Abstract: Molecular simulations reveal how graphene grows on copper surfaces, and that defects in the graphene structure are continually removed by mobile copper atoms in the surface layer of the catalyst.
Structural and energetic trends in Group-I and II hydrohelide cations
Publisher: Elsevier BV
Date: 11-2008
Synthesis, characterisation and structure determination of 3-[(1Z)-{2-[bis({[(2-methylphenyl)methyl]sulfanyl})methylidene]hydrazin-1-ylidene}methyl]benzene-1,2-diol
Publisher: Elsevier BV
Date: 11-2018
o-Vanillin Derived Schiff Bases and Their Organotin(IV) Compounds: Synthesis, Structural Characterisation, In-Silico Studies and Cytotoxicity
Publisher: MDPI AG
Date: 15-02-2019
DOI: 10.3390/IJMS20040854
Abstract: Six new organotin(IV) compounds of Schiff bases derived from S-R-dithiocarbazate [R = benzyl (B), 2- or 4-methylbenzyl (2M and 4M, respectively)] condensed with 2-hydroxy-3-methoxybenzaldehyde (oVa) were synthesised and characterised by elemental analysis, various spectroscopic techniques including infrared, UV-vis, multinuclear (1H, 13C, 119Sn) NMR and mass spectrometry, and single crystal X-ray diffraction. The organotin(IV) compounds were synthesised from the reaction of Ph2SnCl2 or Me2SnCl2 with the Schiff bases (S2MoVaH/S4MoVaH/SBoVaH) to form a total of six new organotin(IV) compounds that had a general formula of [R2Sn(L)] (where L = Schiff base R = Ph or Me). The molecular geometries of Me2Sn(S2MoVa), Me2Sn(S4MoVa) and Me2Sn(SBoVa) were established by X-ray crystallography and verified using density functional theory calculations. Interestingly, each experimental structure contained two independent but chemically similar molecules in the crystallographic asymmetric unit. The coordination geometry for each molecule was defined by thiolate-sulphur, phenoxide-oxygen and imine-nitrogen atoms derived from a dinegative, tridentate dithiocarbazate ligand with the remaining positions occupied by the methyl-carbon atoms of the organo groups. In each case, the resulting five-coordinate C2NOS geometry was almost exactly intermediate between ideal trigonal-bipyramidal and square-pyramidal geometries. The cytotoxic activities of the Schiff bases and organotin(IV) compounds were investigated against EJ-28 and RT-112 (bladder), HT29 (colon), U87 and SJ-G2 (glioblastoma), MCF-7 (breast) A2780 (ovarian), H460 (lung), A431 (skin), DU145 (prostate), BE2-C (neuroblastoma) and MIA (pancreatic) cancer cell lines and one normal breast cell line (MCF-10A). Diphenyltin(IV) compounds exhibited greater potency than either the Schiff bases or the respective dimethyltin(IV) compounds. Mechanistic studies on the action of these compounds against bladder cancer cells revealed that they induced the production of reactive oxygen species (ROS). The bladder cancer cells were apoptotic after 24 h post-treatment with the diphenyltin(IV) compounds. The interactions of the organotin(IV) compounds with calf thymus DNA (CT-DNA) were experimentally explored using UV-vis absorption spectroscopy. This study revealed that the organotin(IV) compounds have strong DNA binding affinity, verified via molecular docking simulations, which suggests that these organotin(IV) compounds interact with DNA via groove-binding interactions.
Comparison of single-walled carbon nanotube growth from Fe and Ni nanoparticles using quantum chemical molecular dynamics methods
Publisher: Elsevier BV
Date: 09-2010
Oxygen Vacancy Defect Migration in Titanate Perovskite Surfaces: Effect of the A-Site Cations
Publisher: American Chemical Society (ACS)
Date: 24-05-2018
How does acetonitrile modulate single-walled carbon nanotube diameter during CVD growth?
Publisher: Elsevier BV
Date: 05-2019
Nanostructure, hydrogen bonding and rheology in choline chloride deep eutectic solvents as a function of the hydrogen bond donor
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C6CP07932F
Abstract: Ab initio MD and experiments are combined to reveal how the nanostructures in choline chloride deep eutectic solvents, and hence their properties, are modulated by the hydrogen bond donor structure.
Formation of persistent organic pollutants from 2,4,5-trichlorothiophenol combustion: a density functional theory investigation
Publisher: Springer Science and Business Media LLC
Date: 14-05-2016
DOI: 10.1007/S00894-016-2987-Z
Abstract: Polychlorinated dibenzothiophene (PCDT) and polychlorinated thianthrene (PCTA) are sulfur analogues of dioxins, such as polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/F). In this work, we present a detailed mechanistic and kinetic analysis of PCDT and PCTA formation from the combustion of 2,4,5-trichlorothiophenol. It is shown that the formation of these persistent organic pollutants is more favourable, both kinetically and thermodynamically, than their analogous dioxin counterparts. This is rationalised in terms of the different influences of the S-H and O-H moieties in the 2,4,5-trichlorothiophenol and 2,4,5-trichlorophenol precursors. Kinetic parameters also indicate that the yield of PCDT should exceed that of PCDD. Finally, we demonstrate here that the degree and pattern of chlorination on the 2,4,5-trichlorothiophenol precursor leads to subtle thermodynamic and kinetic changes to the PCDT/PCTA formation mechanisms. Graphical abstract Formation mechanisms of persistant organic pollutants, PCDT and PCTA, from 2,4,5-trichlorothiophenol combustion, has been investigated using density functional theory.
QM/MD Simulation of SWNT Nucleation on Transition-Metal Carbide Nanoparticles
Publisher: American Chemical Society (ACS)
Date: 20-10-2010
DOI: 10.1021/JA106264Q
Abstract: The mechanism and kinetics of single-walled carbon nanotube (SWNT) nucleation from Fe- and Ni-carbide nanoparticle precursors have been investigated using quantum chemical molecular dynamics (QM/MD) methods. The dependence of the nucleation mechanism and its kinetics on environmental factors, including temperature and metal-carbide carbon concentration, has also been elucidated. It was observed that SWNT nucleation occurred via three distinct stages, viz. the precipitation of the carbon from the metal-carbide, the formation of a "surface/subsurface" carbide intermediate species, and finally the formation of a nascent sp(2)-hybidrized carbon structure supported by the metal catalyst. The SWNT cap nucleation mechanism itself was unaffected by carbon concentration and/or temperature. However, the kinetics of SWNT nucleation exhibited distinct dependences on these same factors. In particular, SWNT nucleation from Ni(x)C(y) nanoparticles proceeded more favorably compared to nucleation from Fe(x)C(y) nanoparticles. Although SWNT nucleation from Fe(x)C(y) and Ni(x)C(y) nanoparticle precursors occurred via an identical route, the ultimate outcomes of these processes also differed substantially. Explicitly, the Ni(x)-supported sp(2)-hybridized carbon structures tended to encapsulate the catalyst particle itself, whereas the Fe(x)-supported structures tended to form isolated SWNT cap structures on the catalyst surface. These differences in SWNT nucleation kinetics were attributed directly to the relative strengths of the metal-carbon interaction, which also dictates the precipitation of carbon from the nanoparticle bulk and the longevity of the resultant surface/subsurface carbide species. The stability of the surface/subsurface carbide was also influenced by the phase of the nanoparticle itself. The observations agree well with experimentally available data for SWNT growth on iron and nickel catalyst particles.
Rovibrational Spectra of LiH2+, LiHD+ and LiD2+ Determined from FCI Property Surfaces
Publisher: American Chemical Society (ACS)
Date: 25-04-2007
DOI: 10.1021/JP066369D
Abstract: Full configuration interaction (FCI) has been used in conjunction with the lithium [6s5p3d1f] (Iron, M. A. et al. Mol. Phys. 2004, 101, 1345) and hydrogen aug-cc-pVTZ basis sets to construct an 83-point potential energy surface of the 1A1 ground state of 7LiH2+. Vibrational and rovibrational wave functions of the (6,7)LiH2+, (6,7)LiHD+, and (6,7)LiD2+ ground states were calculated variationally using an Eckart-Watson Hamiltonian. For (7)LiD2+, rovibrational transition frequencies for K = 0, 1, 2 and J < or = 10 are within ca. 0.1% of recent experimental values (Thompson, C. D. et al. J. Chem. Phys. 2006, 125, 044310). A 47-point FCI dipole moment surface was embedded in the rovibrational Hamiltonian to calculate vibrational and rovibrational radiative properties. At 296 K, with v < or = 4 and J < or = 4, the 2(02) band was found to have the greatest spectral intensity with respect to the ground electronic states of (6,7)LiH2+, (6,7)LiHD+, and (6,7)LiD2+. In each case, the most intense rovibrational transitions have been assigned unequivocally using the J, Ka, Kc assignment scheme.
Catalytic CVD synthesis of boron nitride and carbon nanomaterials – synergies between experiment and theory
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C7CP03835F
Abstract: We present a perspective demonstrating the importance of synergy between experiment and theory for modern nanomaterial synthesis.
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